High-frequency conductor having a low impedance movable electrical contact device



Nov. 16, 1948. HQLMAN ETAL 2,454,062

HIGHFREQUENCY CONDUCTOR HAVING A LOW IMPEDANCE MOVABLE ELECTRICAL c'onmc'r DEVICE Filed Oct. 2, 1943 5 shuts-Shea: 1

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Q15 7 l Zgv4 1 19a INVENTORS HERBERT EDWARD HOLMflN EDWARD CFC CORK ATTORNEY Nov. 16, 1948. H. HOLMAN M; 2,454,062

NG A LOW IMPEDANCE HIGH-FREQ CY DUCTOR HAVI MOVAB ELECTRICAL CONTACT DEVICE Filed Oct. 2, 1943 3 Sheets-Sheet 2 INVENTORS EDWARD CFC/L com BY )%%m HE/QBERT EDWARD HOLMA/V Nov. 16, E948. H. E. HOLMAN ETAL 5 HIGH-FREQUENCY CONDUCTOR HAVING A LOW IMPEDANCE MOVABLE ELECTRICAL CONTACT DEVICE Filed Oct. 2, 1943 3 Sheets-Sheetfi INVENTORS HERBl-RT sow/m0 HOLMAN ion/Aka CFC/L CORK ATTORNEY HIGH-FREQUENCY CONDUCTOR HAVING A LOW IMPEDANCE MOVABLE ELECTRICAL CONTACT DEVICE Herbert Edward Holman, West Drayton, and Edward Cecil Cork, Ealing, London, England, assignors to Electric & Musical Industries Limited, Hayes, Middlesex, England, a company of Great Britain Application October 2, 1943, Serial No. 504,744 In Great Britain December 1'7, 1940 Section 1, Public Law 690, August 8, 1946 Patent expires December 17, 1960 7 Claims.

1 This invention relates to apparatus for use with high frequency electrical oscillations and more particularly to apparatus comprising cylindrical conductors with or without a concentric inner conductor. of the piston.

In the measurement of electrical impedances In order that the invention may be more at high frequencies, it is frequently convenient Clearly understood, it will now be described by to employ apparatus comprising a cylindrical Way of example with reference to certain figures conductor and one or more conducting pistons of the drawing which show apparatus incorposlidable within said conductor so as electrically rating the invention which is suitable for use in to close one or both ends thereof. A central the measurement of impedances at high freconductor may also be provided within said q S. cylindrical conductor to form therewith a coaxial ig. 1 of the drawing shows a front elevation line. Such apparatus may be used for example of the ve tion partly in diagram form; as a resonator or oscillator for high frequencies. Fig. 2 is a front elevation of the device of It is clearly important that such apparatus shall this invention; be so designed that the piston makes good elec- 3 is a detail P y in section showing trical contact with the inner surface of the t e a an t f t piston n t ndu tor; cylinder and also with the central conductor if 4a is a P specti V W showing the Piston such be provided so that substantially no variain detail; tions in the resistance or inductance of the con- 4b is an end elevation O nections shall occur when the piston is moved. 4C is a side elevation 0f the P It is therefore the object of the present inveni 5 is a cross-sectional V w f the clamp tion to provide apparatus in which movable elecembracing the 0111561 c r, the section being trical connections which are consistently of low taken 11 0f F resistance and inductance may be effected be- Fig. 6a is a sectional view of a circular p st tween a conducting piston and the inner surface Which is divided along a p ane no mal 130 its of a cylindrical conductor and also if desired axis, the Sect n being taken on l e 6 -6 of between said piston and a central conductor b; within said cylindrical conductor, Fig. 6b is a cross-sectional view taken on line According to the invention, there is provided 0f apparatus for use with high fresuency electrical Fig. 7a is a plan view of an alternative type oscillations comprising a cylindrical conductor, of piston;

a conducting piston slidable within the cylindri- Fig. 7b is across-sectional View taken on line cal conductor and a clamp embracing the cylin- 5 'l-"l of Fig. a; drical conductor, the arrangement being such Fig. 8a is a plan view of a piston having a j that when said clamp is tightened electrical conseries of slots located at its periphery;

tact of low impedance at said high frequency is Fig. 8b is a side elevation of Fig. 8a; established between the inner surface of said Fig. 9 is a circuit diagram of the device of this cylindrical conductor and said piston. invention; and

The clamp may conveniently be arranged to Fig. 10 is a circuit diagram of the invention. move with the piston by means of a mechanical Fig. 1 shows the general circuit arrangement coupling therebetween so as always to lie subof the invention, the upper portion of which is stantially in the plane of said piston. shown as having the outer conductor I and the If desired, a further conductor may be supinner conductor 2 in circuit diagram form, toported centrally within said cylindrical conductor gether with the showing of a condenser 5, varithus forming a coaxial line, and said piston may able inductances 6 and I, a crystal rectifier 8, be arranged to slide thereon and to effect electria crystal rectifier coupling device 9, a flexible cal contact of low impedance at said high freouter conductor H3, and inner conductor H. quency between the further conductor and the '50 Referring now in detail to Figs. 2, 3', 4 and inner surface of the conducting cylinder. 5 of the above mentioned drawings, the apy In order to increase the area of contact, the paratus comprises a cylindrical or outer concylindrical conductor and, if desired, said piston ductor l within which a further or inner conmay be slotted so as to permit the contacting ductor 2 is centrally supported. A piston 3 surfaces to be more readily deformed. 56 (shown in detail in Figs. 4a, 4b and 4c) is ar- 2 The piston may comprise two or more interleaving parts so arranged that when said clamp is tightened the further conductor is clamped between two or more of the interleaving parts ranged to slide on said outer'ccnductor 2 within said conductor I, and a clamp 4 embracing outer conductor I (shown in detail in Fig, is mechanically coupled so as to slide with said piston 3 and always to remain substantially in the plane of the piston. The conductor 2 is conveniently in the form of a wire or rod (which may have a diameter of 1 mm.) which is stretched along the axis of said cylindrical conductor I (which may conveniently have an internal diameter of 5 mm.) and should be formed from a material of good electrical conductivity, such as copper, brass, silver or nickel, and at the same time should be sufificiently thin to afford flexibility for a reason which will hereinafter be explained. The piston 3 is attached to a tube I2 sliding on the conductor 2, and the tube I2 is also attached to the knob I3, which is in turn attached to the rods I4 passing through the fixed block I5 and attached to the clamp 4; Thus, when the knob I3 is moved, the piston 3 and the clamp 4 move together in such a manner that the clamp 4 always surrounds the piston 3.

Referring now to Figs. 4a, 4b and 4c, the piston 3. is in the form of a short conducting circular cylinder provided with a slot normal to its axis and extending inwards from the periphery to a line just beyond a diameter thereof. A semicircular conducting flat segment I6 is housed within this slot. The outer curvature of the segment I6 is substantially equal to the inner curvature of the conductor I, and the chord of the segment is provided with a semi-circular recess having a diameter substantially equal to that of the conductor 2. The segment I6 may be temporarily fixed in position by means of a service pin passed through the holes IGa in the piston 3 and the segment I6 so that the assembly can be ma chined to fit the bore of the cylinder I. The periphery of the piston 3 adjacent the segment I6 is then further machined away so as to allow the segment I6 to project beyond the periphery of the piston (as shown in Fig. 4b) to ensure that when inward radial pressure is applied, the segment will be pressed into firm contact with the conductor 2. It will be appreciated that the service pin is removed prior to inserting the piston 3 into the conductor I.

The purpose of the clamp 4 and the flexible walls of the conductor I will now be appreciated. When the clamp 4 is tightened so as to apply inward radial pressure to the conductor I., the walls thereof are slightly deformed so as to conform to the curvature of the lower half of the piston 3 and the segment I6, and electrical contact of low impedance for high frequency currents is thus made between the inner surface of conductor I and the piston 3 due to the large area of contact of said inner surface with the piston 3 and the segment I6. Further, said conductor 2 is firmly clamped between said piston 3 and said segment I6, and electrical contact of low impedance also efiected between the piston 3 and the conductor 2. Thus, electrical contact of low impedance is effected between said conductors I and 2 through the piston 3. 1

As will be seen from Fig. 5, the clamp 4 may be of known type and may consist of two members each having a semi-circular face of substantially the same curvature as the external surface of the conductor I and arranged to be urged towards each other so as to apply inward radial pressure to said conductor. If the bore of the conductor I is appreciably larger than the dimeter of the piston 3, it will tend to distort'elliptically when clamped. If desired, the clamp may be constructed so as to be in contact with, say, only of the periphery of the conductor I, thus localizing the distortion of the walls thereof and retaining a large area of contact. Alternatively, the conductor I may be provided with a slot parallel to its axis, if electrical considerations permit, so as to reduce the tendency of elliptical distortion. It will be appreciated that it is desirable that the piston 3 and segment I6 be constructed so as to fit accurately in the conductor I, in order to limit as far as possible the distortion of the walls of the cylinder I when clamped.

Alternative forms of piston may be used, and further examples will now be described.

Referring to Figs. 6a and 6b, a circular piston is shown divided into two parts along a plane normal to its axis, one part having a spigot !I arranged to enter a recess in the other part, this spigot I! being of such a length as to provide a space between the two parts of the piston. Fit-ted between these two parts are two square section D-shaped brass springs I-Q bent as shown, so that the central portions of the springs are adapted to press on the conductor 2 and the outer limbs are adapted to slide on the inner surface of the cylinder I, the two halves of the piston being held together by screws or rivets passing through the spigot I]. It will be seen that the spigot I1 is slotted diametrically to provide space for the D-shaped springs I9. It is advantageous to lap the circumferential parts of the springs I9, when assembled in place, by sliding I the whole assembly in a hole of the same diameter as the tube, bored in a suitable cast iron block.

If fine abrasives are used, it will be found possible to obtain contact over the entire spring surface. A similar technique may be employed regard to the conductor 2 by abrasive lapping wit-h awire or rod of the same size as that of the conductor 2 to be used. By these and similar methods .a relatively large area of contact surface may be obtained. This type of piston does not necessarily require the use of a split *or deformed cylinder, as it provides the necessary elasticities by its special construction. It is necessary that the two D-shaped springs have an accurate fit in the axial direction, as otherwise variaticns'of resistance may occur by virtue -.of the fact that the resistance and inductance of the springs may be altered by variation of pressure against the retaining flanges of the piston. In order to eliminate such variations :and also to avoid resistance rand inductance changes due to the piston flanges themselves forming part of the circuit, the piston flanges or body may be made of an insulating material.

Alternatively, the type of piston shown in Fig. 7 may be used. This consists of a short circular cylinder of an electrically conducting material which is turned to the bore of the conductor I and has a central hole of the same size :as the conductor 2. It is provided with a tubular extension which may be a part of the actuating tube I2. The piston .is divided by a suitable number of radial slots extending through part of the extension in order to afford radial elasticity. It will .be obvious that if the conductor I .is contracted, the split form of the piston will enable it to close tightly on to the conductor 2 and thus establish good contact between conductor I and conductor 2.

The above mentioned types of piston are primarily suitable forsmall bore tubes, for example,

20 min. downwards. In cases where larger'bores are used, the construction shown in Fig. 8 is to be preferred. In Fig. 8 the piston 3 consists of a flat disc of conducting metal having reasonably good electric properties, this disc being provided at its periphery with a series of slots as shown, the slots being provided around the center aperture. The degree of elasticity is determined by the angle and length of the slots.. This is permitted in the case of the slots at the periphery by the natural convergence of the slots, but in the case of the slots around the central aperture the elasticity is controlled by the provision of holes drilled through the piston, as shown, and which terminate the slots. The slots of the piston may be substantially covered by a closely fitting cover plate 20 on each side, these plates being of such diameters as to clear both the tube bore and the central rod. The plates should not be allowed to clamp the segments, but should slightly clear them, in order to allow for flexible operation. It will be appreciated that pistons of this type will provide a good contact with the inner surface of the conductor I even if this is not truly circular. As cylinders having large bores are often constricted non-uniformly when radially compressed, such elasticity is of particular advantage.

It will be understood that although the conductors I and 2 have been shown as having circular sections, conductors having rectangular or other sections may be used if desired.

It will also be understood that although in the arrangement described the cylindrical conductor I is associated with a central conductor 2, the invention may also be used in apparatus in which such central conductors are not employed. For example, the invention can be applied to wave guides which comprise a, cylindrical conductor having one or more conducting pistons slidable therein. In such cases it is of course unnecessary to provide for electrical contact between the cen-. ter of said piston and a control conductor. The invention may be applied to apparatus intended for use for purposes other than the measurement of impedance. For example, as shown in Fig. 9, it may be used for mixing two oscillations of different frequency, as in superheterodyne reception. In this case, the side tube 6 of Fig. 1 may be omitted, and a screened feeder Illa, Iflb may be led in through pistons 3a and 3b, respectively, and the inner conductors II a, Ilb thereof arranged to effect a sliding electrical contact on the central wire 2. The two oscillations to be mixed are fed in along the screened feeders IBa, Iilb, and the spacing between the inner faces of the pistons 3a and 3b and the points at which contact is made upon the central wire by the inner conductors I Ia, I Ibis so chosen as to avoid reflections due to impedance mismatch. The position of the pistons 3a, 3b in relation to the position of the capacity 9 feeding the detector 8 is adjusted so that a high impedance is presented to the detector 8 and, if desired, the impedance of the detector 8 may effectively be matched to the central conductor 2 by spacing the pistons 3a, 3?) from the detector 8 by different distances while maintaining the electrical length of the cylinder between said pistons substantially constant. A circuit tuned to the difference of frequency between the oscillations to be mixed is connected in the output of the detector 8, and in operation currents will be set up in said circuit.

In another application shown in Fig. 10, the invention may be applied to apparatus for coupling a source of high frequency oscillations to an output circuit. High frequency oscillations de-' veloped, for example, in the resonant cavity 20 of a velocity modulated electron discharge device or the like, induce currents in the loop M which is connected between the cylinder I and the inner conductor 2. The piston 3 is adjusted to tune the system to resonance, which may convenientlybe indicated'by the detector 8 in the side tube 5. The side tube 6 may then form the outer conductor of an output feeder, the inner con ductor of this feeder being connected to the inner conductor 2. The side tube 6 should join the cylinder I at a point such that the impedance of the feeder is matched to the resonant system. The coupling to the resonant cavity 20 may be controlled by varying the size of the coupling loop or varying the length and position of the loop within the cavity.

It will be appreciated that apparatus constructed according to the invention may be used generally in the measurement, generation, detection or amplification of high frequency electrical oscillations.

What we claim is:

1. Apparatus for use with high frequency electrical oscillations comprising a cylindrical conductor, a conducting piston having a slot, a flat conducting segment housed within said slot, said slot, said piston and said segment being slidable within said cylindrical conductor, a slidable clamp embracing the outer surface of said cylindrical conductor, the arrangement being such that when said clamp is tightened, electrical contact of low impedance at said high frequency is established between the inner surface of said cylindrical conductor and said piston.

2. A high frequency measuring device comprising an outer conductor, an inner conductor, a piston arranged to slide on said inner conductor, a tube having one end secured to said piston and also arranged to slide on said inner conductor, a clamp located externally of said outer conductor, mechanical coupling means for said clamp secured to the other end of said tube to clamp said piston on said inner conductor and maintain an electrical contact between it and the inner surface of the outer conductor and said piston which is of low impedance at high frequencies.

3. A high frequency device for electrically closing an end of a concentric line, comprising an outer conductor, an inner conductor, a piston arranged to slide on said inner conductor, said outer conductor having a slot to permit the contacting surfaces to be more readily deformed to increase the area of contact with the outer periphery of said piston, a tube having one end secured to said piston and also arranged to slide on said inner conductor, a clamp located externally of the outer conductor, mechanical coupling means for said clamp secured to the other end of said tube to clamp said piston on said inner conductor and to maintain good electrical contact between it and the inner surface of the outer conductor.

4. Apparatus for use with high frequency electrical oscillations comprising a cylindrical conductor, a conducting piston including a plurality of interleaving parts and a clamp embracing said cylindrical conductor, the arrangement being such that when the clamp is tightened, electrical contact of low impedance at the said high frequency is established between the inner surface of said cylindrical conductor and said piston.

5. A high frequency device comprising an outer conductor, an inner conductor, a piston having a plurality of radial slots arranged to slide on said inner conductor, and means external of the outer conductor to clamp said piston on said inner con-.- ductor and to maintain electrical contact between it and the inner surface of the outer conductor and said piston which is of low impedance at high frequencies.

6. Apparatus for use with high frequency elec: trical oscillations comprising a cylindrical conductor, a. conducting piston slidably arranged Within said cylindrical conductor, a slidable clamp embracing the outer surface of said cylindrical conductor, said piston being mechanically coupled to said clamp so as to move therewith and to insure that said clamp remains substantially in the same plane as said piston.

7. Apparatus for use with high frequency electrical oscillations comprising a cylindrical outer conductor, an inner conductor centrally secured within said outer conductor, a conducting piston having a slot, a fiat conducting segment housed within said slot, said piston and said segment be- CITED The following references are of record in the file ofthis patent:

NI E S E$ A'I NTS Number Name Date 2,203,806 Wolf June 11, 1940 ,28 ,5 0 B rrow M y 5; 1 20 2,288,516 Davis et al. June 30, 1942 2,335,591 Hansell Nov. 30, 1943 

